How can I use a single action to trigger animations in multiple objects?
Ok I solved this myself and in fact for my problem I didn't even need to use the action editor or NLA editor, all I needed to do was make the bits I wanted as separate animations happen at different points on the timeline, and then when I put the object into unity I could select those frames from the animation to be separate animations, so the whole thing was a lot less complicated than I was trying to make it.
If anyone else has information on how to do this in blender though please add an answer because I'm sure not everyone who comes across this question will be intending on putting their animation into unity and so may still need another answer